Date: Fri, 11 Mar 2005 13:14:38 -0800 From: Julian Elischer <julian@elischer.org> To: Gleb Smirnoff <glebius@freebsd.org> Cc: net@freebsd.org Subject: Re: Giant-free polling [PATCH] Message-ID: <42320A3E.1020708@elischer.org> In-Reply-To: <20050311142805.GB88801@cell.sick.ru> References: <20050311110234.GA87255@cell.sick.ru> <E1D9kbt-000FAj-00._pppp-mail-ru@f22.mail.ru> <20050311141450.GF9291@darkness.comp.waw.pl> <20050311142805.GB88801@cell.sick.ru>
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Gleb Smirnoff wrote: >On Fri, Mar 11, 2005 at 03:14:50PM +0100, Pawel Jakub Dawidek wrote: >P> On Fri, Mar 11, 2005 at 04:55:25PM +0300, dima wrote: >P> +> I thought about using list also, but considered it to bring >P> +> too much overhead to the code. The original idea of handling arrays >P> +> seems to be very elegant. >P> >P> Overhead? Did you run any benchmarks to prove it? >P> I find list-version much more elegant that using an array. > >It is also a small cookie for future. Now we have IFF_POLLING flag and >IFCAP_POLLING, which indicate whether interface support polling and whether >it actually does polling. This is not nice, from my viewpoint. I'd like >to see only IFCAP_POLLING present and turning polling on/off for particular >interface should be done by inserting/removing iface from polling list. > >This will also remove an extra unlocked check of interface flags (?). > >P> I also don't like the idea of calling handler method with two locks >P> held (one sx and one mutex)... > >I agree with Pawel. We have LOR here between sx lock and driver lock: > > normal polling: (get sx shared) -> (get driver mutex) > driver stop: (get driver mutex) -> (get sx exclusive) > >We will have deadlock if this two things process in parallel. > >And the per-interface mutex protects only reentrancy of interface poll >method, is that right? > >P> There is still an unresolved problem (in your and our patch as well) of >P> using ifnet structure fields without synchronization, as we don't have >P> access tointerface's internal mutex, which protects those fields. > > you need to add an interface method that has access to it.. >This is unresolved in our patch, too, and I believe throughout many >other places in kernel. > > >
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